New aspects of the biology of the Melanesian rfhinoceros beetle Scapanes australis (Col., Dynastidae) and evidence for field attraction to males

Scapanes australis is a major coconut pest, endemic in Papua New Guinea. Early in the night, males placed singly into artificial galleries made in young coconut palms exhibited a sex specific calling behaviour for 1 to 1.5 h. Coming to the gallery entrance, they raised the abdomen and the hind legs, the head lowered inside the gallery, and emitted a liquid secretion, rhytmically smeared by crossing the legs. Females which did not behave so, were very mobile. The adult flying period coincided with the male calling behaviour. In field assays with caged insects on coconut palms, attraction of both sexes to males was evidenced when they were calling. Males fought for gallery possession at a male arrival. No aggression but mating was observed with arriving females, which proved not to have developed oocytes. The strong male attractionwas confirmed using automatic traps, baited with one lived male in a sugarcane piece. Male were assumed to release an aggregation pheromone. Further studies are underway to identify the putative pheromone.     

Ecological methods for adult populations of Oryctes rhinoceros (Coleoptera, Scarabaeidae)

ABSTRACT. 1. For comparing assessment methods, O.rhinoceros (L.) populations were monitored in five 30–50 ha plots in southern Luzon, Philippines. No consistent correlations were found between number of beetles caught in traps, amount of palm damage and number of breeding sites. Apparently, plots were too small to account for fast dispersal of beetles.
2. Coconut cap traps baited with ethylchrysanthemumate attracted O.rhinoceros adults searching for breeding sites. Several factors were identified influencing catches but trapping was found to be unsuitable for accurately assessing pest populations.
3. A new method which gives estimates on the monthly number of O.rhinoceros attacks on coconut palms, was tested in the Maldives. Palms are climbed about once a year and the sequence of fronds, the number and the position of beetle cuts are recorded.
4. Reduction with age of the length of three teeth on the fore tibia of O. rhinoceros adults was studied in the Philippines. The data was insufficient to obtain a clear correlation between age and length of teeth.
5. The observations indicated that in the Philippines after leaving their site of pupation, O.rhinoceros adults spend about 5 weeks feeding on coconut palms. This is followed by a period of about 7 weeks in breeding sites and, on occasion, additional visits to palms. With these estimates it was possible to relate palm damage records with numbers of feeding adults.     

Pupation site and emergence time influence the mating success of bagworm females,Oiketicus kirbyi

In commercial oil palm plantations in Costa Rica, we tested the hypotheses that pupation site and emergence time affect the mating success of protogynous female bagworms,Oiketicus kirbyi (Guilding) (Lepidoptera: Psychidae). Greater proportions of female than male pupae on upper leaves of oil palms and greater proportions of mated females in the upper rather than lower crown strata support the hypothesis that selection of pupation site by female larvae influences the mating success of adults. Increasing captures of males with increasing trap height further suggest that enhanced mating success of females in tree tops may be attributed either to most effective dissemination of sex pheromone on higher sites, or to males foraging predominantly in the upper strata of oil palms. As the majority of females pupated in the middle rather than upper crown of oil palms, selection of pupation site by females may be affected by additional as yet unknown factors. Emergence of females significntly preceded emergence of males. Increasing proportions of mated females throughout the emergence seasons probably resulted from an increased ‘availability’ of males. In tropical rainforests with local variations inO. kirbyi developmental time and stage, protogyny may represent an evolutionary strategy that furthers outbreeding.     

Zophiuma lobulata (Hemiptera: Lophopidae) causes Finschhafen disorder of coconut and oil palms

Finschhafen disorder (FD) affects coconut and oil palms in Papua New Guinea (PNG). It is characterised by yellow‐bronzing of fronds which begins at the tips and progresses towards the petiole. Although the planthopper Zophiuma lobulata (Hemiptera: Lophopidae) has been posited as a cause of FD, the basis of the relationship has not been established. Studies conducted previously on FD predate the availability of DNA‐based techniques to test for the involvement of plant pathogens such as phytoplasmas that cause yellows‐type diseases in many plant taxa and are transmitted by the order of insects to which Z. lobulata belongs. In this study, polymerase chain reaction (PCR) assays found no evidence of phytoplasmas or bacteria‐like organisms (BLOs) in tissues of coconut and oil palm symptomatic for FD and from Z. lobulata feeding on these plants. Further studies involved releasing Z. lobulata adults and nymphs onto caged, potted coconut and oil palms and onto palm fronds enclosed in mesh sleeves. In both experiments, chlorotic symptoms on the palms were observed in the presence of Z. lobulata. Insect‐free control palms did not exhibit chlorotic symptoms of FD. In the frond sleeve experiment, only the fronds where Z. lobulata fed developed chlorosis indicating that the disorder is not systemic. Unlike most yellows‐type diseases associated with Hemiptera, this study indicates that FD is because of a direct feeding effect on palms by Z. lobulata rather than transmission of a pathogen.     

Female moths of cotton bollworm (Lepidoptera: Noctuidae) captured by waterbasin traps baited with synthetic female sex pheromone

Cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), is one of the most important pest insects in cotton fields in China. Female moths were captured by waterbasin traps with a synthetic female sex pheromone blend in cotton fields over three years. The blend contained (Z)‐11‐hexadecenal and (Z)‐9‐hexadecenal with a ratio of 97:3. Each pheromone dispenser was impregnated with 2.0 mg of pheromone blend and 0.2 mg of antioxidant dissolved with 0.1 mL of hexane, and there was a control dispenser with a similar amount of antioxidant and solvent only. Waterbasin traps were deployed in three configurations in the fields. ‘A’ was pheromone traps only, ‘B’ was both pheromone and control traps, ‘C’ was control traps only. (i) In four plots of ‘A’, the average weekly female catch was 1.5, and more females were captured by centrally located pheromone traps, (ii) In three plots of ‘Brsquo;, control traps also captured female as well as male moths, but average weekly female catches of control traps was significantly lower than that in pheromone‐baited traps. (iii) There were significant linear relationships between the average weekly female catch and the corresponding layer in pheromone‐baited traps in both ‘A’ and ‘B’ plots, and in quadratic equations in control in ‘B’ plots. (iv) With the increase of the interval of traps, average weekly female catches per trap increased but average weekly female catches per hectare decreased. (v) Among the female moths captured by pheromone traps, 88.3% were mated female moths which each containing 1.46 spermatophores, while in control traps 86.9% of the mated female moths had 0.90 spermatophores. There was a significant difference between the average numbers of spermatophores of mated females in pheromone traps and in controls.     

Should I stay or should I go? Modelling dispersal strategies in saproxylic insects based on pheromone capture and radio telemetry: a case study on the threatened hermit beetle <Emphasis Type="Italic">Osmoderma eremita</Emphasis>

To predict how organisms cope with habitat fragmentation we must understand their dispersal biology, which can be notoriously difficult. We used a novel, multi-pronged approach to study dispersal strategies in the endangered saproxylic hermit beetle Osmoderma eremita, exploiting its pheromone system to intercept high numbers of dispersing individuals, which is not possible with other methods. Mark-release-recapture, using unbaited pitfall traps inside oak hollows and pheromone-baited funnel traps suspended from tree branches, was combined with radio telemetry (in females only) to record displacements. Dispersal, modelled as a probability distribution of net displacement, did not differ significantly between sexes (males versus females recaptured), observation methods (females recaptured versus radio-tracked), or sites of first capture (pitfall trap in tree versus pheromone trap – distance from original dispersal point unknown). A model including all observed individuals yielded a mean displacement of 82 m with 1% dispersing > 1 km. Differences in body length were small between individuals captured in pitfall versus pheromone traps, indicating that dispersal is rarely a condition-dependent response in O. eremita. Individuals captured in pheromone traps were consistently lighter, indicating that most dispersal events occur relatively late in life, which agrees with trap catch data. In addition, most (79%) females captured in pheromone traps were mated, showing that females typically mate before leaving their natal tree. Our data show that integrating odour attractants into insect conservation biology provides a means to target dispersing individuals and could greatly improve our knowledge of dispersal biology in threatened species.     

Flight movement of Scapanes australis australis (Boisduval) (Coleoptera: Scarabaeidae: Dynastinae) in Papua New Guinea: a radiotelemetry study

Abstract We used radiotelemetry and/or chemical light-tags to track the flight of 15 individuals of Scapanes australis in Madang Province, Papua New Guinea. This species causes severe economic impacts on coconut palms in young plantations. Flights to feeding, mating, resting, and possibly oviposition sites covered distances of 52 to 835 m in males, and from 245 m to>1000 m in females. Upon release, females flew in a tight upward spiral above canopy level (>20 m), then usually flew along a single bearing out of radio reception within 1 min of initiating flight. Dispersing females probably follow scent trails to pheromone-releasing males that occupy feeding galleries excavated most frequently in coconut palms, or search for oviposition sites. Most tagged females were not found again, because they dispersed beyond the tracking capabilities of our radio-receivers, but one female was followed for 245 m to a feeding gallery excavated by an adult male. Males typically flew within 5 m of the ground, took erratic flight paths with numerous turns, and frequently circled coconuts and other host plants. We followed males from the release point until they ceased flight for a night. Males passed daylight hours either in a feeding gallery within a host plant or under soil litter.     

Olfactometer Responses of Plum Curculio <Emphasis Type="Italic">Conotrachelus nenuphar</Emphasis> (Herbst) (Coleoptera: Curculionidae) to Host Plant Volatiles,Synthetic Grandisoic Acid,and Live Conspecifics

The plum curculio Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) is a major pest of pome and stone fruit, but will also attack other fruits. Males produce the aggregation pheromone grandisoic acid; emitting only the (+)-enantiomer which is attractive to both sexes of the univoltine and multivoltine strains, while the synthetic racemic mixture contains optical isomers with equal amounts of (+)- and (?)-enantiomers. Synergy between odours can increase trap captures and improve monitoring techniques, therefore tests were performed in a dual-choice olfactometer with odours attractive to plum curculios according to literature to determine 1) under what physiological conditions (mating status, age, starvation period) these odours are attractive or repulsive, 2) if the (+)-enantiomer or the odour of live males synergizes with host plant volatiles, and 3) if there is a difference in response between plum curculio strains. Females were exposed to: benzaldehyde; trans-2-hexenal; apples; extracts of: plums, apples, blueberries; grandisoic acid; and live males. Plum essence was found to be the most attractive host-plant odour for both immature and mature virgin females, and immature whole apples were attractive to starved females, while trans-2-hexenal, McIntosh apple essence, benzaldehyde along with the combination of benzaldehyde and plume essence was found to be repulsive. Starvation, age, and mated status all influence response to odours. No synergistic or additive affects were observed between any of the odour combinations tested, including the combination of both the natural and synthetic pheromone and plum essence or apples.     

Ovarian development of Agrilus planipennis: effects of age and mating status and influence on attraction to host volatiles

Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a major pest of ash trees, Fraxinus spp. (Oleaceae), in North America. This study investigated the timing of reproductive development in female beetles and the influence of female reproductive maturity on attraction to host volatiles. Based on dissections of females of increasing age, females with access to males for mating, and thus presumed mated, developed mature eggs only after 18–24 days. In contrast, female beetles reared without access to males, and thus unmated, did not develop mature eggs at any age. Chemical analysis of cuticular hydrocarbons detected the contact sex pheromone, 9‐methyl‐pentacosane, in cohorts of females which were 8–9 days old and older, supporting previous research that this compound signals sexual maturity to males. Results from field‐trapping bioassays demonstrated that stage of female reproductive maturity influenced their attraction to host volatiles: females caught on traps baited with foliar volatiles contained eggs and ovarioles that were significantly less developed than those on traps baited with bark sesquiterpenes. However, our results revealed that females with immature stages of ovarioles and undeveloped eggs, such as those observed in unmated females, were rarely ever caught on traps baited with either of the host volatile lures. Further research on host compounds attractive to immature females is critical for early detection and possible control of A. planipennis populations during the extended pre‐oviposition period.     

Ecology of baculovirus-infected and healthy adults of Oryctes rhinoceros (Coleoptera: Scarabaeidae) on coconut palms in the Philippines

Abstract.

• 1 Males and females of Oryctes rhinoceros (L.), a serious pest of coconut palms, congregate in decaying coconut trunks to mate, oviposit and prepare the wood for the young larvae. A baculovirus disease is often transmitted from beetle to beetle in this environment and transmission to and from larvae probably also occurs.
• 2 Young beetles are mainly found feeding on palms, where they also frequently contract the virus disease, presumably through mating with diseased partners.
• 3 Monitoring beetle populations in the Philippines with attractant traps and by collections from palms showed seasonal fluctuations which were often inversely correlated with the incidence of the virus disease. Disease prevalence matched closely the proportion of females in the population. Possible explanations for this correlation and for the seasonality of the disease prevalence are outlined.

     

Identification of the Aggregation Pheromone of the Melon Thrips,Thrips palmi

The objective of this study was to identify the aggregation pheromone of the melon thrips Thrips palmi, a major pest of vegetable and ornamental plants around the world. The species causes damage both through feeding activities and as a vector of tospoviruses, and is a threat to world trade and European horticulture. Improved methods of detecting and controlling this species are needed and the identification of an aggregation pheromone will contribute to this requirement. Bioassays with a Y-tube olfactometer showed that virgin female T. palmi were attracted to the odour of live males, but not to that of live females, and that mixed-age adults of both sexes were attracted to the odour of live males, indicating the presence of a male-produced aggregation pheromone. Examination of the headspace volatiles of adult male T. palmi revealed only one compound that was not found in adult females. It was identified by comparison of its mass spectrum and chromatographic details with those of similar compounds. This compound had a structure like that of the previously identified male-produced aggregation pheromone of the western flower thrips Frankliniella occidentalis. The compound was synthesised and tested in eggplant crops infested with T. palmi in Japan. Significantly greater numbers of both males and females were attracted to traps baited with the putative aggregation pheromone compared to unbaited traps. The aggregation pheromone of T. palmi is thus identified as (R)-lavandulyl 3-methyl-3-butenoate by spectroscopic, chromatographic and behavioural analysis.     

Isolation ofAcholeplasma spp. from coconut palms affected by lethal yellowing disease in Jamaica

A total of 35 isolates ofAcholeplasma spp. were recovered from phloem sap and rotting tissues of lethal yellowing-diseased coconut palms. The highest isolation rate, 33% of samples from two palms, was obtained in a conventional mycoplasma medium supplemented with Tween 80; no isolates were recovered from healthy palm tissues or from uninoculated media constituents. Metabolic and serological tests on uncloned isolates showed that about two-thirds were strains ofA. axanthum and the remainder were related toA. oculi. These results strongly suggest that acholeplasmas occur in or on plant tissues either as pathogens, epiphytes, or saprophytes.     

Phytoplasma distribution in coconut palms affected by lethal yellowing disease

Lethal yellowing (LY), the most devastating disease affecting the coconut palm in America, is caused by phytoplasmas known to be distributed in different parts of infected plants. However, no comprehensive reports exist on the phytoplasma distribution. This study refers to the detection of LY phytoplasma DNA using PCR in different coconut plant parts, throughout the development of the disease. Sample analysis of positive palms taken at different stages of disease development (either symptomatic or symptomless) showed differences in the percentage of LY detection between plant parts. Some parts showed a very high level of LY DNA (stem, young leaves, inflorescences, stem apex and root apex), low levels were found in the intermediate leaves and roots without apex, whereas no LY phytoplasma DNA was detected in mature leaves. The detection percentage of LY phytoplasma DNA was lowest in symptomless‐infected palms for all parts, except the stem, where phytoplasma accumulations were consistently detected. This pattern of detection among parts is consistent with the hypothesis that phytoplasmas move from photosynthate source tissues to sink tissues via the phloem mass flow process. The accumulations in the (lower) stem, prior to the appearance of symptoms, suggest that this part of the palm is where phytoplasmas first move from leaves after foliar feeding by vectors and in which they probably multiply and distribute to other palm parts, including roots. Embryos from infected palms were analysed by nested‐PCR and 28% of 394 embryos were positive. Phytoplasma DNA was detected in embryos from fruit on any of the fruiting bunches regardless the age, but no pattern of quantitative distribution throughout the bunch developmental stages was observed. Germination of seeds from LY‐positive symptomatic palms was 58% and from LY‐negative symptomless palms were 71%. No phytoplasma was detected in seedlings tested from both symptomatic and non‐symptomatic palms. Seedlings tested after 2 years did not develop LY symptoms or eventually died.     

Physiological development and dispersal ability of newly emerged Monochamus galloprovincialis

Novel associations between exotic pathogens and native insects may result in major ecological and economical losses. In Europe, Monochamus galloprovincialis (Olivier) (Coleoptera: Cerambycidae) is the only known vector of the exotic pine wood nematode Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle (Nematoda: Aphelenchoididae), the causal agent of pine wilt disease (PWD). Transportation of goods containing nematode‐infested beetles is the main pathway for the spread of the disease. In this scenario, management actions involving early detection and eradication are critical to stop further spread by the vector. Although dispersal of mature M. galloprovincialis has been successfully tracked using commercial baits and traps, dispersal ability of immature individuals is poorly understood. Sexual maturation and other physiological traits related to dispersal were studied for newly emerged M. galloprovincialis after different shoot‐feeding spans. Sexual maturation was complete after on average 12 (males) or 13 (females) feeding days. Monochamus galloprovincialis adults emerged with an average of 10% lipid and 23.8% (males) or 29.9% (females) pterothorax muscle content, and these percentages did not change significantly during shoot feeding. Microtomography images of wing muscle structures at different maturation stages confirmed these results. Emerged adults that were kept unfed survived an average of 12 days in the lab. The ability of unfed immature insects to fly through hostless terrain was studied by marking and releasing newly emerged insects from a crop area located up to 3 km away from two small pine stands. The longest flown distance recorded was 2 km. Fitted regressions indicated that immature insects could have travelled up to 3 109 m to reach the experimental stands. We found that M. galloprovincialis emerge with well‐developed thoracic muscles and energy reserves that enable them to sustain long flights over non‐forested areas. These findings should aid managers and policy makers in devising sound procedures in areas where the risk of introducing PWD is high.     

Pheromonal cross-attraction in true bugs (Heteroptera): attraction of Piezodorus hybneri (Pentatomidae) to its pheromone versus the pheromone of Riptortus pedestris (Alydidae)

We investigated the attractiveness of a synthetic form of the pheromone of the soybean stink bug, Piezodorus hybneri (Gmelin), under field conditions, and compared it with that of (E)-2-hexenyl (E)-2-hexenoate, a pheromone component of a competitor, Riptortus pedestris (Fabricius). Many adult stink bugs were attracted to traps baited with 100 mg of the synthetic pheromone (1: 1: one mixture of β-sesquiphellandrene, (R)-15-hexadecanolide, and methyl (Z)-8-hexadecenoate), but few were attracted to 1 or 10 mg. More than twice as many females as males were attracted to this male-produced pheromone. None of the individual pheromone components (30 mg) attracted conspecifics. In summer (June-July), when field P. hybneri were not in diapause, (E)-2-hexenyl (E)-2-hexenoate was more attractive to P. hybneri than the synthetic pheromone. The sex ratio of the adults attracted to the synthetic pheromone was highly female-biased, yet almost equal numbers of both sexes were attracted to (E)-2-hexenyl (E)-2-hexenoate. Most females attracted to both attractants were mated and had mature ovaries. However, adults attracted to (E)-2-hexenyl (E)-2-hexenoate were likely to have less food in their stomach than those attracted to the synthetic pheromone. In late autumn (October-November), when the bugs were in reproductive diapause, both attractants attracted many sexually immature female and male adults that had well-developed fat body. The synthetic pheromone also attracted a large number of conspecific nymphs. These results suggest that P. hybneri pheromone and R. pedestris pheromone component, respectively, have different functions for P. hybneri. The male-produced pheromone system of P. hybneri seems to be sex-related but to have other roles.     

Biology and Structure of Phytomonas staheli sp. n., a Trypanosomatid Located in Sieve Tubes of Coconut and Oil Palms

SYNOPSIS. Phytomonas staheli sp. n. is described from the oil palm ( Elaeis guineensis ) and the coconut palm ( Cocos nucifera ) of Surinam, South America. The phytomonad is the probable cause of "Hartrot" in the coconut palm and "Marchitez sopresiva" in oil palms. Parasites are confined to the sieve tubes in palms. Some success was obtained at cultivation of the organism from Elaeis.     

Modelling female mating success during mass trapping and natural competitive attraction of searching males or females

Simulation models of insects encountering sex pheromone with or without mass trapping in which the searching sex is either male (moths and many insect species) or female (some true bugs, beetles, and flies) were developed. The searching sex moved as a correlated random walk, while the opposite sex remained stationary (calling) and released an attractive sex pheromone. The searching sex was caught when encountering a pheromone‐baited trap, and females mated when encountering a male. An encounter with pheromone was defined by the searcher's interception of a circle termed the effective attraction radius (EAR_c). Parameters of movement (speed and duration), initial numbers of calling sex and searching sex, number of traps, area, and EAR_c of traps and calling sex were varied individually to evaluate effects on the percentage of females mating. In the natural condition without traps, female mating success in both models was identical. Increasing the EAR_c of the calling sex caused diminishing increases in female mating success, suggesting that evolution of larger pheromone release and EAR_c is limited by increasing costs (production/sensitivity) relative to diminishing increases and benefits of mating encounters. With mass trapping, increasing the EAR_c of traps or density of traps caused similar declines in female mating in both models, but the female‐searching model predicted slightly lower mating success than the male‐searching model. Increasing the EAR_c of calling insects or the initial density of insects caused similar increases in female mating in both models, but again the female‐searching model had slightly lower mating success than the male‐searching model. The models have implications for mating lek formation and for understanding the variables affecting the success of mass trapping programs for insect pests with either male or female sex pheromones.     

Response of both sexes of Trichoplusia ni (Lepidoptera: Noctuidae) to virgin females and to synthetic pheromone

Abstract. 1. Male and female Trichoplusia ni were caught at three locations in California in 1974 and 1975, in traps baited with virgin female T. ni or with synthetic female pheromone.
2. 71% of the females were captured between 20.00 and 21.00 hours; only 22% of the males.
3. Both mated and unmated females were trapped.
4. Comparisons of live trap vs. dead trap catches suggest that females are responding to the virgin females (or synthetic pheromone) and not to a combination of stimuli from the first trapped males plus female pheromone.     

Social media posts suggest that coconut rhinoceros beetle has established in the Western hemisphere

The coconut rhinoceros beetle (CRB: Oryctes rhinoceros L.) is one of the most damaging pests of coconut and oil palms in the Asia/Pacific region but has not been reported from the Western Hemisphere. Here, we report a possible establishment of CRB in Nayarit, Mexico, based on an analysis of social media reports and photographs indicating the presence of the beetle and the distinctive v-shaped notches in palm fronds caused by the beetle feeding. CRB populations are destructive once established, therefore, urgent actions are required to contain the pest and prevent damage to coconut and oil palm in the Americas.     

Sex ratio and maturity indicate the local dispersal and mortality of adult stoneflies

1. Despite a recent upsurge in interest, there remains remarkably little information about the dispersal and survival of the adults of most stream‐dwelling insects, although this is a basic requirement for understanding their long‐term population dynamics. 2. Using Malaise traps for a whole annual flight period, we captured adult stoneflies (Leuctra nigra) along transects perpendicular to three upland Welsh streams. We assessed spatial and temporal patterns in sex ratio to infer local dispersal and, using maturity as an age marker, estimated the mortality of adult females. 3. Nearly all adult stoneflies (99%) were taken in the period 26 April–23 July, and the onset of the male and female flight periods was the same. Most males (90%) had been caught by late June. Females were classified as immature (without ripe eggs) or mature, and 90% of immature females had been caught by mid‐late June (depending on catchment). As immature females declined in the catch, mature females increased, 10% having been caught by late‐May to early June and 90% by early to mid‐July. The median catches of immature and mature females were separated by 32 days in all three catchments. 4. There was a female bias in the sex ratio overall, which increased as time passed and was attributable partially to the greater longevity of females. Late in the flight period, however, female bias was also greater near the stream channel implying a return of mature females (but not males) from the riparian vegetation, presumably to oviposit. 5. The number of mature females was less than the number of immatures in two of the three channels. Over all three catchments, the overall mortality of females over the 32 days taken to mature was estimated at 29%, equivalent to an exponential daily rate of 1.1% day^?1. The apparently negative mortality rate in one catchment (i.e. more matures than immatures being caught) could be due to an influx of adult females from elsewhere along the channel to oviposit. 6. Natural markers of age and population structure, such as sex ratio and female maturity, thus enabled us to detect a return of females to the stream to oviposit, after prior limited dispersal into the riparian zone, and to infer longitudinal movements in search of suitable sites. We were also able to estimate mortality in the field. Such natural markers seem to have been underexploited in the study of adult aquatic insects.